Silicon die

A silicon die is the actual circuit inside a chip: a thin rectangle of silicon, from about a millimeter to a few centimeters across, carrying transistors and the wiring that connects them. It's what you'd find if you dissolved away the black plastic of a chip.

It's built on the wafer in two big stages. First, the transistors are made in the silicon surface, from thousands to billions per die. Then comes the wiring, built in layers above them, often ten or more. For each layer, a film of low-k dielectric insulator is deposited, and trenches and holes are etched into it through light-patterned masks. The trenches are lined with a few nanometers of tantalum, which stops copper atoms from drifting into the silicon and ruining transistors. Then copper is electroplated in to fill them, and the top is polished flat, ready for the next layer. Finally, the wafer is tested, thinned and cut into separate dies with a diamond saw or laser.

Different designs become different chips: the system-on-chip, memory, storage, display drivers, the infrared receiver and many other integrated circuits. Copper wiring replaced aluminum in leading chips starting in the late 1990s.